Mobile phase— Dissolve 0.20g of monobasic potassium phosphate and 0.45mLof n-heptylamine in about 350mLof water.Adjust with phosphoric acid to a pHof 3.0,dilute with water to 400mL,add 600mLof acetonitrile,and mix.

Standard preparation— Dissolve an accurately weighed quantity of USP Dyclonine Hydrochloride RSin 0.001Nphosphoric acid to obtain a solution having a known concentration of about 0.1mg per mL.

Assay preparation— Transfer an accurately measured portion of Gel,equivalent to about 5.0mg of dyclonine hydrochloride,to a 50-mLvolumetric flask.Add 10mLof 0.001Nphosphoric acid,and sonicate to dissolve the gel.Dilute with 0.001Nphosphoric acid to volume,and mix.

Chromatographic system (see Chromatography á621ñ)—The liquid chromatograph is equipped with a 254-nm detector and a 4-mm ×25-cm column that contains 5-µm diameter packing L13.The flow rate is about 1.2mLper minute.Adjust the flow rate,if necessary,so that the retention time of dyclonine hydrochloride is not less than 5minutes.Chromatograph five replicate injections of the Standard preparation,and record the peak responses as directed for Procedure:the tailing factor is not more than 2.0and the relative standard deviation is not more than 3.0%.

Procedure— Separately inject equal volumes (about 20µL)of the Standard preparationand the Assay preparationinto the chromatograph,record the chromatograms,and measure the responses for the major peaks.Calculate the quantity,in mg,of dyclonine hydrochloride (C18H27NO2·HCl)in the portion of Gel taken by the formula: in which Cis the concentration,in mg per mL,of USP Dyclonine Hydrochloride RSin the Standard preparation,and rUand rSare the peak responses obtained from the Assay preparationand the Standard preparation,respectively.